This invention relates generally to systems for position detection and ranging, and, more particularly, relates to apparatus and methods for precise determination of the position of multiple movable objects, utilizing transmission and detection of electromagnetic energy.
Position detection and tracking of movable objects is useful in a wide variety of applications, including construction site vehicle tracking, fleet vehicle dispatch and monitoring, courier monitoring, industrial robot control, tracking of animal migration, monitoring of human operatives or mechanical devices in remote areas, and battlefield command and control.
A number of systems have been proposed or constructed for monitoring the position of movable objects by dispatch personnel, or for advising vehicle operators of instantaneous position. Conventional LORAN systems, for example, carried by air- and seacraft, inform the pilot of vehicle position with respect to multiple transmitters situated at known, fixed locations. In these systems, measurement of distance between the vehicle and transmitters is implemented by comparison of phase between arriving signals. The following U.S. and foreign patents and patent applications disclose various position measurement or detection systems.
______________________________________ Cain et al. 4,756,617 Cain et al. 4,732,471 Win et al. 4,730,190 Reinaud 4,703,820 Petersen 4,676,634 Cain et al. 4,674,870 Ikeda et al. 4,674,054 Christy et al. 4,665,404 Van de Velde et al. 4,659,982 Izutani et al. 4,658,257 Sekine 4,644,358 Huck, Jr. et al. 4,630,685 Cain et al. 4,600,997 Miller et al. 4,537,502 von Pieverling 4,536,763 Ward 4,488,154 Buck et al. 4,453,825 Wind 4,433,335 Hammada et al. 4,413,904 Vachenauer et al. 4,319,243 Etsusaki et al. 4,273,196 Hill et al. 4,171,907 Brenner 4,140,060 Zindler 4,119,379 Endo 4,110,754 Roeder et al. 4,106,017 Roeder et al. 4,103,302 Martens 4,021,116 Halajian et al. 3,864,513 Cornsweet 3,864,030 Funk et al. 3,775,735 Hotston 3,757,330 Heflinger 3,743,418 Ross 3,652,161 Studebaker 3,588,249 Green 1,750,668 German 3,311,349 German 3,234,446 German 2,853,317 German 2,620,809 Great Britain 2,076,152 Soviet Union 742,844 East Germany 229,866 ______________________________________
The Ikeda et al. patent discloses a radio system for automatic control and positioning of machinery. The system includes high frequency inductive radio cables located in pairs along the paths taken by the machines. The cables are connected to address detectors and transceivers in a centrally controlled system. Each machine is provided with a radio and antenna for receiving commands from the controller. The controller detects the location of each machine, as indicated by phase shift of the lines.
The Christy et al. patent discloses a positioning system including base stations having a clock, and a circuit synchronized with the clock for transmitting a spread-spectrum signal. A mobile station comprises a clock synchronized with the base station clock. A circuit receives the spread signal and compares the timing of the signal to the timing of the mobile station clock for producing a phase difference signal indicative of range from a base station.
Van de Velde et al. discloses a microwave system including microwave receiving antennas and at least one correlator. A radiating antenna emits microwave radiation from a source having predetermined characteristics. The transmitted microwave signal is received by antennas at different locations, and circuits are provided to measure the time elapsed between two zero crossings of the received signals.
Sekine discloses an orientation measurement apparatus including an antenna for receiving global positioning system (GPS) radio waves and devices for rotating the antenna. Circuitry is provided for detecting the orientation of GPS satellite by detecting phase differences of the received wave during a period of rotation of the antenna.
Huck, Jr. et al. discloses apparatus for controlling a bulldozer or other earthmoving equipment. The apparatus evaluates longitudinal angular velocity of a bulldozer to control the position/elevation of the bulldozer blade.
Miller et al. discloses a target ranging system including a carrier frequency transmitter and a generator for generating at least two modulating signals for modulating the carrier. A receiver is provided for receiving a reflected signal from the target and for producing a corresponding received electrical signal. A phase detection device detects phase differences between the modulating signals and each of the received signals, and a data processor utilizes the detected phase differences to calculate range.
Ward discloses a radar processor including circuitry for deriving signals from reflections of directively radiated groups of at least three radar pulses in which the interpulse periods in each group are equal.
Buck et al. discloses an electronic distance meter which measures distance to a moving target by comparing the phase of a signal propagated to the target with the phase of the reflected signal.
Wind discloses a transmitter locating apparatus including circuitry for receiving electromagnetic radiation from the transmitter. The radiation is demodulated individually from each of plural receivers. A digital computer Fourier transforms the demodulated radiation and provides signals representing the radiation as a function of frequency. An additional computing device establishes a signal representing the phase difference between the demodulated radiation from each of the signals. The apparatus correlates signal timing differences to a hyperbolic surface of rotation on which the transmitter is located.
Vachenauer et al. discloses a system for determining the position of vehicles by measuring reception time differences. An area is scanned by a narrow beam from an electronically steered phased array antenna driven by the interrogating transmitter of a secondary radar system. A receiving antenna, remote from the interrogator and its beam, is similarly scanned. The identifying response from a transponder in a vehicle is received, and the vehicle position is computed from the differences between the times of reception, utilizing a hyperbolic algorithm.
Etsusaki et al. discloses a system for automatically maintaining the blade of an earthmoving machine in a predetermined relationship to a reference beam. A beam receiver, mounted on a rotatable shaft attached to the blade, includes vertically arrayed beam receiving elements for generating a signal representative of beam height. In response to the detected signal, actuators coupled to the blade raise and lower the blade to vertically align the beam receiver with the beam.
Hill et al. discloses an electro-optical distance measuring device including circuits for generating a light signal that is amplitude modulated by three selectable frequencies. Optics focus the modulated light onto the target, and receive reflection of the light therefrom. Additional circuits convert the received light to electrical signals representative of the light, and compute the phase angles between these signals and the amplitude modulating signals. The distance to the target is calculated from these phase angles.
Brenner discloses an optical system wherein pulses of optical energy are intensity modulated by a radio frequency subcarrier and transmitted to a moving target. Reflected pulses from the target are received, and target velocity information is generated from the doppler frequency shift of the radio frequency subcarrier of the return pulses.
The Roeder '017 and '302 patents disclose velocity sensors using a transmitter on an aircraft to direct a radar beam at an object. A receiver mounted on the aircraft receives reflected pulses through an antenna which has forward and aft phase center locations. A computer system performs a time/amplitude comparison of the signals detected at the aft phase center location against the signal detected at the forward phase center location a selected interval earlier in time.
Martens discloses electro-optical distance measuring apparatus for measuring the distance between a moving object and a stationary object. The apparatus includes circuitry for generating a series of cyclic radiation fringe patterns, which vary in correspondence with movement of the object being observed.
Hotston discloses an interferometer for measuring the distance to a moveable object. The interferometer includes a waveguide for radiating energy toward the object and for receiving energy reflected from the object.
Ross discloses distance measuring apparatus in which distance is measured by detecting the travel time of an energy pulse, using a measuring signal which is short relative to the distance being measured.
Green discloses apparatus for measuring the position of moving objects, including elements for transmitting, between fixed and moving stations, electromagnetic signals whose phase is related to a frequency generated at the fixed station. A comparison is made between the phase of the signal generated at the fixed station and the phase of a signal which has been shifted in phase by transmission. The position of the moving object is calculated from the phase adjustment necessary to bring the compared frequency components into phase with each other.
The German 3,311,349 publication discloses a position measurement system in which an optical receiver mounted on a vehicle is interrogated using a laser source. The laser source emits two encoded laser beam "barriers" in which each individual beam has both fixed and angle dependent laser beam modulation frequencies. The receiver provides a reference frequency, which is phased to the fixed source frequency. The receiver includes circuitry for measuring the time of receipt and the polarization direction of both modulation frequencies. Speed, direction and distance are determined from phase differences, receive times, and angles.
German 2,620,809 discloses a system for automatic position monitoring and control of an earthmover blade. A computer, utilizing information from angle transducers located on the earthmoving machine, compares the actual angles of elements of the blade to predetermined values required to create an embankment having a selected slope. In response, actuators regulate the motion and position of the blade to provide the selected embankment slope.
East German 229,866 discloses apparatus in which a hyperbolic position calculation is executed. The arrangement includes a command center, at least three measurement stations, and a mobile transmitter which is to be located. Transit time difference is measured by phase comparison and processed to enable a determination of mobile transmitter location.
Conventional systems typified by the disclosures of these publications, however, typically fail to provide rapid, precise, inexpensive measurement of the position of multiple movable objects in three spatial dimensions. Certain conventional position detection systems are hampered by data communications channels unable to provide high-speed multiple signal processing for precise, real-time ranging and position detection of multiple objects. Additionally, many conventional position detection and ranging systems require that each movable object be fitted with a relatively complex and expensive transceiver.
It is thus an object of the invention to provide position detection methods and apparatus which enable rapid, precise determination of object position in three spatial dimensions.
A further object of the invention is to provide position detection methods and apparatus which are relatively simple and economical to implement, wherein the bulk of electronic complexity and cost is allocated to a single base station, and wherein multiple target transceivers can be deployed at optimally low cost.
Another object of the invention is to provide such methods and apparatus which can utilize existing communications channels and apparatus.
Other general and specific objects of the invention will in part be obvious and will in part appear hereinafter.